#include<iostream>
#include<cstdio>
#include<algorithm>

using namespace std;

using LL = long long;

int main()
{
	LL res = 1;
	for (int i = 2020, j = 1; j <= 4; i--, j++)
		res = res * i / j;

	cout << res << endl;
	return 0;
}